Starting device for a single-phase asynchronous motor

ABSTRACT

The invention relates to a starting device for a single phase asynchronous motor comprising an auxiliary winding. The device includes first and second glow discharge lamps with each lamp having a thermal switch and these lamps being in series with the auxiliary winding. The first lamp has a glow discharge current established by current flowing in the auxiliary winding. The first lamp switch has normally closed contacts and the second lamp switch has normally open contacts. A resistor in shunt with the second lamp causes ignition of the second lamp when crossed by a predetermined supply voltage. The second lamp switch is closeable after a time lag due to a glow discharge current of said second lamp. The first lamp switch is openable after a time lag when a maximum line current is established when said second line switch is closed. The resistor causing extinguishing of the second lamp when a minimum voltage drop thereacross is established by a minimum line current consisting only of said first lamp discharge current.

United States Patent [191 Laursen STARTING DEVICE FOR A SINGLE-PHASE ASYNCHRONOUS MOTOR [76] inventor: Gorm Laursen, Ahornsvej 6, 6400 Sonderborg, Denmark 22 Filed: Sept. 4, 1973 21 Appl. No.: 394,391

[30] Foreign Application Priority Data Primary Examiner-B. Dobeck in] 3,846,683 [4 1 Nov. 5,1974

[5 7] ABSTRACT The invention relates to a starting device for a single phase asynchronous motor comprising an auxiliary winding. The device includes first and second glow discharge lamps with each lamp having a thermal switch and these lamps being in series with the auxiliary winding. The first lamp has a glow discharge current established by current flowing in the auxiliary winding. The first lamp switch has normally closed contacts and the second lamp switch has normally open contacts. A resistor in shunt with the second lamp causes ignition of the second lamp when crossed by a predetermined supply voltage. The second lamp switch is closeable after a time lag due to a glow discharge current of said second lamp. The first lamp switch is openable after a time lag when a maximum line current is established when said second line switch is closed. The resistor causing extinguishing of the second lamp when a minimum voltage drop thereacross is established by a minimum line current consisting only of said first lamp discharge current.

1 Claim, 2 Drawing Figures STARTING DEVICE FOR A SINGLE-PHASE ASYNCHRONOUS MOTOR The series resistor causes the first glow discharge lamp, containing the starting switch proper, to carry a reduced discharge current upon completion of the starting operation. This limitation of the current results in a lower current density. This leads to the desired longer service life. The second glow discharge lamp ensures that the series resistor is noneffective during the starting-up period, i.e. that it does not also reduce the starting current flowing through the auxiliary winding.

The circuit components used and their rating ensure that the starting operation proceeds automatically.

The invention will now be described in greater detail by reference to the annexed drawing, in which:

FIG. 1 is a circuit diagram of a single phase asynchronous motor having the starting device in accordance with the invention, and

FIG. 2 shows in a time diagram various characteristics occurring during the starting operations.

An asynchronous motor 1 has a main winding 2 and and an auxiliary winding 3. An A.C. voltage U is supplied to these windings from mains terminals 5 and 6 through a main switch 4.

The starting device has, in series with the secondary winding 3, a first flow discharge lamp 7 and a parallel arrangement consisting of a series resistor 8 and a second glow discharge lamp 9. The first glow discharge lamp 7 has a thermal or bimetal switch of which the normally closed contacts open after a time lag under the effect of the current flowing through it, and are held open under the effect of the glow discharge then occurring. The glow discharge lamp 9 has a normally open thermal or bimetal switch 11, of which the contacts close after a time lag under the effect of the glow discharge, are held closed under the effect of the current flowing therethrough, and open as soon as this current falls below a minimum value.

When the main switch 4 is moved to the on position, the following cycle takes place. At first there occurs in the auxiliary winding circuit a current that is determined only by the resistances of the auxiliary winding 3 and the series resistor 8. The voltage drop at the series resistor 8 is greater than the ignition voltage of the second glow discharge lamp. The latter ignites. As a consequence of the glow discharge the switch 11 closes after a predetermined time lag T Since the two switches 10 and 11 are closed, the full starting current flows through the auxiliary winding 3. Under the effect of this current, the switch 10 of the first glow discharge lamp 7 opens after a predetermined time lag T The current in the starting circuit is reduced to a value which corresponds to the discharge current in the glow discharge lamp 7 which is usual in the known circuits.

During all this time the thermal switch 11 of the sec-' ond glow discharge lamp 9 will have been kept closed by the heating effect of the starting current flowing through it. Since upon opening of the switch 10 of the first glow discharge lamp 7 the current drops below the minimum value necessary for keeping the switch 11 closed, the latter opens. Thus, the series resistor 8, hitherto short circuited, is rendered effective. The discharge current in the first glow discharge lamp 7 drops to a corresponding value which is lower than in the known starting devices of this kind. As a result of the matching between the resistance of the series resistor 8 and the ignition voltage of the glow discharge lamp 9, the voltage drop now occurring at the series resistor 8 does not suffice to ignite the glow discharge lamp 9 again or to keep it ignited. This second glow discharge lamp 9 is therefore not effective during the running of the machine, nor is it loaded by a glow discharge.

When the motor 1 is switched off, the glow discharge in the glow discharge lamp 7 ceases. The thermal switch 10 closes again. The starting device has thus reached its initial condition.

If, when the contacts of the switch 11 are opened, the glow discharge lamp 9 tends to ignite again, it suffices to rate a series resistor 8 in such manner that when the contacts of the first glow discharge lamp 7 are opened, the voltage drop is smaller than the glow voltage of the glow discharge lamp 9.

In the time diagram of H6. 2, various characteristics explained in detail below, are shown against time t.

A. shows the switching positions of the main switch 4, i.e. the open positions a and the closed position b. The closed time can be divided into the starting time T during which the starting device executes various switching operations, and into the normal operating time T during which the starting device has reached its operational at-rest position.

B. shows the contact position of the glow discharge lamp 9. After a time lab T the contacts move from the open position a into the closed position b and remain in this position until the starting time T ends. C.

c. shows the contact position of the glow discharge lamp 7. The contacts remain in their closed position b until the time lag T has elapsed after closing of the contacts 11, whereupon the contacts move into their open position a.

D. shows the current through the auxiliary winding 3. The full starting current d flows only during the time lag T During the remaining time in which the main switch 4 is closed there flows a very much smaller current d which corresponds to the discharge currents in the glow discharge lamp 9 and 7 respectively (compare the characteristic values E and F).

E. shows the glow discharge, i.e., the glow discharge current e in the glow discharge lamp 9. It occurs only during the time lag T F. shows the glow discharge, i.e., the glow discharge current in the glow discharge lamp 7. This current has a normal value g from the end of the time lag T to the end of the starting time T,,-. During the normal operating time T however a reduced value f occurs.

G. shows the voltage drop at the series resistor 8. During the first time lag T, this voltage drop has a high value i which is greater than the ignition voltage of the glow discharge lamp 9. During the normal operating time T however there occurs a small value h which is lower than the ignition voltage of the glow discharge lamp 9.

I claim:

1. A starting device for a single phase asynchronous motor comprising an auxiliary winding, first and second glow discharge lamps each having a thermal switch, said lamps being in series with said winding, saif first lamp having a glow discharge current established by current flowing in said auxiliary winding, said first lamp switch having normally closed contacts and said second lamp switch having normally open contacts, a resistor lished when said second line switch is closed, said resistor causing extinguishing of said second lamp when a minimum voltage drop thereacross is established by a minimum line current consisting only of said first lamp discharge current. 

1. A starting device for a single phase asynchronous motor comprising an auxiliary winding, first and second glow discharge lamps each having a thermal switch, said lamps being in series with said winding, saif first lamp having a glow discharge current established by current flowing in said auxiliary winding, said first lamp switch having normally closed contacts and said second lamp switch having normally open contacts, a resistor in shunt with said second lamp for causing ignition of said second lamp when crossed by a predetermined supply voltage, said second lamp switch being closeable after a time lag due to a glow discharge current of said second lamp, said first lamp switch being openable after a time lag when a maximum line current is established when said second line switch is closed, said resistor causing extinguishing of said second lamp when a minimum voltage drop thereacross is established by a minimum line current consisting only of said first lamp discharge current. 